I saw these canaries foraging in the shrubbery alongside the Abrahamskraal hide in WCNP on 28 September 2010. While they are apparently not at all uncommon, they were a new sighting for me — and I've not seen them since

All juv canaries are streaked and your pic is at a very difficult angle, showing little of what one can use to make a good ID.

The two main contenders are white-throated and black-headed. The bill on this bird does not seem heavy enough to be WTC and I cannot see any eyebrow. So, yes, it appears that you have got it right all along!

Just as a matter of interest, for ID purposes side-on and rear views provide the most ID features... With this bird I will not argue if another 'mite offers a different opinion.